1. Field of the Invention
The present invention generally relates to a bi-level positive airway pressure support system, and, more particularly, to a bi-level pressure support system and method of providing bi-level pressure support in which the rise time from the expiratory phase of pressure support to the inspiratory phase is automatically adjusted.
2. Description of the Related Art
Pressure support systems that provide a flow of breathing to an airway of a patient at an elevated pressure to treat a medical disorder are well known. One basic form of pressure support system is a continuous positive airway pressure (CPAP) system, which typically involves providing a flow of breathing gas, such as air, to a patient""s airway at a constant pressure throughout a patient""s breathing cycle. When used to treat obstructive sleep apnea (OSA), for example, this constant pressure is provided at a level sufficient to overcome a patient""s airway resistances.
It is also known to provide a bi-level positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient""s breathing cycle. In a bi-level pressure support system, an inspiratory positive airway pressure (IPAP) is provided during a patient""s inspiratory phase of the breathing cycle and an expiratory positive airway pressure (EPAP) is provided during the expiratory phase. The EPAP is lower than the IPAP so that the patient exhales against relatively low pressure as compared to the IPAP pressure, thereby increasing the comfort to the patient. The BiPAP(copyright) family of pressure support devices manufactured by Respironics, Inc. of Murrysville, Pa., are examples of pressure support device that provide this bi-level form of pressure support therapy. In addition, several U.S. patents describe this bi-level pressure support system in detail, including U.S. Pat. Nos. 5,433,193; 5,313,937; 5,239,995; and 5,148,802, all of which are hereby expressly incorporated herein by reference as if set forth in their entirety herein.
With the improved effectiveness of bi-level pressure support systems over their progeny, CPAP systems, the emphasis has shifted to creating bi-level pressure support systems that are more comfortable for a patient to use without sacrificing treatment effectiveness. It is anticipated that a more comfortable pressure support system will be more frequently and more correctly used by the patient.
U.S. Pat. No. 5,927,274 discloses a bi-level pressure support system that transitions from EPAP and IPAP over a rise time interval, which typically has a length of several hundreds of milliseconds. The ""274 patent provides the operator with the ability to manually adjust this rise time interval to increase patient comfort. While the manual rise time selection technique taught by the ""274 patent is a step toward increasing patient comfort, it is also burdensome, because the operator must manually adjust the rise time setting as needed via a control input on the pressure support device. This can require numerous adjustments over relatively short periods of time if patient comfort is to be optimized. It can be appreciated that there is perceived a need for a pressure support system with increased patient comfort with little or no resultant decrease in therapy effectiveness and that minimizes the amount of operator intervention required to implement the improved pressure support therapy effectively.
Accordingly, it is an object of the present invention to provide a bi-level pressure support system that overcomes the shortcomings of conventional pressure support systems. This object is achieved according to one embodiment of the present invention by providing a bi-level pressure support system that includes a pressure generating system that produces a flow of breathing gas at an inspiratory positive airway pressure and an expiratory positive airway pressure. A conduit delivers the flow of breathing gas to an airway of a patient. A sensor detects a physiological condition of the patient, such as whether the patient is experiencing a breathing disorder. A control system controls the output of the pressure generating system to automatically adjust the rise time from the inspiratory positive airway pressure to the expiratory positive airway pressure based on the output of the sensor. Preferably, the control system increases the rise time in the absence of breathing disorders to increase patient comfort.
It is yet another object of the present invention to provide a method of providing bi-level pressure support that does not suffer from the disadvantages associated with conventional pressure support techniques. This object is achieved by providing a method that includes producing a flow of breathing gas at an inspiratory positive airway pressure and an expiratory positive airway pressure that is less than the inspiratory positive airway pressure, detecting a physiological condition of a patient receiving the flow of breathing gas, and determining a rise time from the inspiratory positive airway pressure to the expiratory positive airway pressure based on the physiological condition of the patient. The rate of change from the inspiratory positive airway pressure to the expiratory positive airway pressure is controlled based on this rise time.
These and other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.